This invention relates to a photographic objective lens system and more particularly the invention is concerned with providing a symmetrical arrangement of optical elements suitable for transferring the image on a cathode ray tube face plate to a photographic film at 1:1 magnification with a high level of chromatic correction in the highly dispersive spectral region from 0.40 to 0.52 microns wavelength.
The design of the thick meniscus anastigmats is a complex undertaking because of the close inter-relationship of all the variables. In general, the exterior shape and thickness are chosen to control the Petzval sum, and the distance from the stop can be used to adjust the astigmatism. However, the adjustment of element powers to correct chromatic aberration inevitably upsets the balance, as does the bending of the entire meniscus to correct spherical. What is necessary is one simultaneous solution for the relative powers, thicknesses, bendings and spacings. The efforts of designers in this direction over many years have produced many good representative designs which can be improved by utilizing the newer types of optical glass such as the rare earth glasses. The introduction of new types of glasses containing rare earths has led to lens elements which for the same power have weaker surfaces and are, therefore, capable of achieving more favorable conditions.
It would be especially desirable and a step forward in the art to provide a photographic objective lens which is particularly suitable for transferring the image on a cathode ray tube face to a photographic film at a 1:1 magnification. A lens suitable for this purpose must provide a high level of optical imaging quality over the entire format of the tube face. In order to accomplish this, particular glass types, number of elements and the use of thicknesses greater than usual are required to produce the high quality image of the phospor tube. Also, the particular glass types should permit a high level of chromatic correction in the highly dispersive spectral region from 0.40 to 0.52 microns wavelength.